A hematoma block is a relatively noninvasive method of analgesia in preparation for relocation of a displaced fracture. The procedure involves the injection of a local anesthetic into a collection of blood that has extravasated into the soft tissue between two fragments of displaced bone. This extravasated blood exists because of damage to the blood vessels within the fractured bone. With injection of a local anesthetic into this "pool" of blood", painless manipulation of the involved fragments of bone is achieved, thus sparing the patient from more invasive analgesic techniques such as conscious sedation and the risks associated with that.
First, identify where the displaced fracture is. This is sometimes obvious when there is a gross deformity, however with more subtle deformities the area where the patient is most tender can help identify the precise location. Next, after the patient's skin has been properly cleaned, advance the needle while aspirating. Positive return of blood indicates correct needle tip placement, and at this point you can instill about 5-10 mL of lidocaine into the site, depending on the patient, where the fracture occurred, and how large the fracture is. Wait about several minutes while the anesthetizing agent takes affect, and proceed with alignment when the patient feels comfortable.